Carlo PaganiMilano & DESY
Report on Fundamental R&D Activities for SRF Accelerators
CSTS du SACMCEA/Saclay, June 3, 2003
Carlo Pagani 2CSTS du SACM
CEA/Saclay, June 3, 2003
SRF before TESLA
From Hasan PadamseeTotal >1000 meters
> 5 GV
Carlo Pagani 3CSTS du SACM
CEA/Saclay, June 3, 2003
A lot of R&D around the world
Understanding MultipactoringA few computer codes developedSpherical shape realized at Genova and qualified at Cornell & Wuppertal
Understanding Field EmissionEmitters were localized and analyzedImproved treatments and cleanness
Cure thermal BreakdownHigher RRR NbDeeper control for inclusions
1984/85: First great successA pair of 1.5 GHz cavities developed andtested (in CESR) at Cornell
Chosen for CEBAF at TJNAF for a nominal Eacc = 5 MV/m
Eacc
> 5 MV/m
Carlo Pagani 4CSTS du SACM
CEA/Saclay, June 3, 2003
Limiting Problems before ’90s
Material propertiesModerate Nb purity (Niobium from the Tantalum production)Low Residual Resistance Ratio, RRR Low thermal conductivityNormal Conducting inclusions Quench at moderate field
Cavity treatments and cleannessCavity preparation procedure at the R&D stageHigh Pressure rinsing and clean room assembly not yet introduced
Microphonics Mechanical vibrations in low beta structures High RF power required
MultipactoringMP has been the major limit for HEPL, and electron linacs to 1984 Pill-box like geometry: higher shunt impedance but higher MP problems
Quenches/Thermal breakdown because of low RRR and NC inclusions
Field EmissionGeneral limit at those time because of poor cleaning procedures and material
Carlo Pagani 5CSTS du SACM
CEA/Saclay, June 3, 2003
The TESLA Challenge
Origin of the name
TESLA Collaboration set up at DESY1992
Physical limit is 50 MV/m > 25 MV/m could be obtainedCommon R&D effort for TESLA
• Higher conversion efficiency• Smaller emittance dilution
Carlo Pagani 6CSTS du SACM
CEA/Saclay, June 3, 2003
The 9-cell TESLA cavityMajor Contributors: CERN, Cornell, DESY, Saclay
- Niobium sheets (RRR=300) are scanned by eddy-currents to detect avoid foreignmaterial inclusions like tantalum and iron- Industrial production of full nine-cell cavities:
- Deep-drawing of subunits (half-cells, etc. ) from niobium sheets- Chemical preparation for welding, cleanroom preparation- Electron-beam welding according to detailed specification
- 800 °C high temperature heat treatment to stress anneal the Nband to remove hydrogen from the Nb- 1400 °C high temperature heat treatment with titanium getter layerto increase the thermal conductivity (RRR=500)- Cleanroom handling:
- Chemical etching to remove damage layer and titanium getter layer- High pressure water rinsing as final treatment to avoid particlecontamination
Figure: Eddy-current scanning system for niobium sheets Figure: Cleanroom handling of niobium cavities
9-cell, 1.3 GHz, TESLA cavity
TESLA cavity parameters
Hz/(MV/m)2≈ -1KLorentz
kHz/mm315∆f/∆l
mT/(MV/m)4.26Bpeak/Eacc
2.0Epeak/Eacc
Ω1036R/Q
Carlo Pagani 7CSTS du SACM
CEA/Saclay, June 3, 2003
Preparation of TESLA Cavities
Carlo Pagani 8CSTS du SACM
CEA/Saclay, June 3, 2003
A pragmatic choice
Define the best cavity treatment procedure based on:Existing experience on different labsOutcomes from the ongoing fundamental R&DCompromise among the different theoriesDiscussions and meetings
Set up of a complete infrastructure with all possible diagnostic to:Limit the human noiseControl all the process parametersGuarantee stable results
Wide use of the fundamental R&D support on samples to understand results and modify the process if required
Stay open to new results and understandings
Carlo Pagani 9CSTS du SACM
CEA/Saclay, June 3, 2003
3rd Cavity Production - BCP
1E+09
1E+10
1E+11
0 10 20 30 40Eacc [MV/m]
Q0
AC55 AC56AC57 AC58AC59 AC60AC61 AC62AC63 AC64AC65 AC66AC67 AC68AC69 AC79
1011
109
1010
3rd Production - BCP Cavities
Cavity AC 67 has a cold He leak
Carlo Pagani 10CSTS du SACM
CEA/Saclay, June 3, 2003
Cavity vertical tests and linac performances
<Eacc> for Q0 ≥ 1010
Module performance in the TTF LINAC
Improved weldingStricter niobium quality control
<Eacc> for Q0 ≥ 1010
Carlo Pagani 11CSTS du SACM
CEA/Saclay, June 3, 2003
Electropolishing for 35 MV/m
• EP developed at KEK by Kenji Saito (origiginally by Siemens)
• Coordinated R&D effort: DESY, KEK, CERN and SaclayFirst electro-polished single cell cavities
BCP Surface (1µm roughness)
BCP Surface (1µm roughness)
0.5 mm
EP Surface (0.1µm roughness)
0.5 mm
Electro-polishing (EP) instead of the standard chemical polishing (BCP) eliminates grain boundary steps Field enhancement.
Gradients of 40 MV/m at Q values above 1010 are now reliably achieved in single cells at KEK, DESY/CERN and TJNAF.
Carlo Pagani 12CSTS du SACM
CEA/Saclay, June 3, 2003
TESLA 800 PerformancesVertical Tests
1E+09
1E+10
1E+11
0 10 20 30 40Eacc [MV/m]
Q0
AC72 epAC73 epAC76 epAC78 ep
1011
109
1010
3rd Production - electro-polished Cavities
TESLA-800 specs: 35 MV/m @ Q0 = 5 × 109
9-cell EP cavities from 3rd productionEP by KEK
1400 °C heat treatment
AC76: just 800 °C backing
Carlo Pagani 13CSTS du SACM
CEA/Saclay, June 3, 2003
TESLA 800 in ChechiaHorizontal Tests
TESLA-800 specs: 35 MV/m @ Q0 = 5 × 109
In Chechia the cavity has all its ancillariesChechia behaves as 1/8th (1/12th) of a TESLA cryomodule
.0E+09
.0E+10
.0E+11
0 10 20 30 40Eacc [MV/m]
Q0
CWCW after 20KCHECHIA 10 Hz ICHECHIA 5 HzCHECHIA 10 Hz IICHECHIA 10 Hz III
AC73 - Vertical and Horizontal Test Results1011
109
1010
Cavity AC73• Vertical tests of naked cavity• Chechia tests of complete cavity
Carlo Pagani 14CSTS du SACM
CEA/Saclay, June 3, 2003
Thanks to TESLA achievements New projects are proposed and funded
200 MHz for Neutrinos
High Energy PhysicsTESLANeutrino Factories and Muon CollidersKaon Beam Separation at FNALNew TEVATRON Injector
Nuclear PhysicsRIA EURISOLCEBAF Upgrade
High Power Proton Linacs for SpallationSNS, Joint-Project, Korea, ESSADS for Waste Transmutation
New Generation Light SourcesRecirculating Linacs (Energy Recovery)SASE FELs
SNS
Carlo Pagani 15CSTS du SACM
CEA/Saclay, June 3, 2003
SNS and TESLA
Push for SRF at the end of 1999TTF Operation Experience Outstanding Results on SC Cavities
Cavity design Electromagnetic DesignMechanical analysisHOM Couplers
Fabrication TechnologyBumb-bells, Stiffening ringsFlanges, Tuners and HOM CouplersTreatments and Handling
Carlo Pagani 16CSTS du SACM
CEA/Saclay, June 3, 2003
The role of Saclay
Inside the TESLA Collaboration the CEA/Saclay group played a fundamental role, being one of the major actors
The activities and results presented at this meeting give a good impression of this role
Carlo Pagani 17CSTS du SACM
CEA/Saclay, June 3, 2003
Nice Historical Synthesis
Carlo Pagani 18CSTS du SACM
CEA/Saclay, June 3, 2003
But…
Fundamental R&D alone is not sufficient to produce accelerator cavities with stable high performances
A strong coordination with the cavity production is required: push the limit inside the boundary conditions
Remember the role of: better Nb material and better rinsing (high pressure rinsing) to push forward the limits for field emission and quench
All the activities should be done, as in the past, in a more wide international collaboration
Carlo Pagani 19CSTS du SACM
CEA/Saclay, June 3, 2003
Fundamental R&D for bulk Nb
It has been crucial in the past to reach stable fabrication procedure for high quality SC Cavities: Eacc > 20 MV/m.
Define crucial material properties: fabrication and controlDefine “standard” cavity fabrication procedure and stabilize specsDefine “standard” BCP receipt and stabilize specsDefine “standard” cleaning techniques and stabilize specs
It is crucial now for TESLA to reach stable fabrication procedure for very high quality SC Cavities: Eacc > 35 MV/m.
Define “standard” EP receipt and stabilize specsDefine optimum heat treatment cycle (600-800 °C) and stabilize specsDefine “standard” backing (100-150 °C) receipt and stabilize specsDefine optimum cycle to cure trapped flux: cure multipactoring
Understand the temperature dependence of Hcrit and try to cure it if Eacc > 40 MV/m is required.
Carlo Pagani 20CSTS du SACM
CEA/Saclay, June 3, 2003
Results from Cornell
Hcrit @ 2 K possibly lower then predictedLimit for TESLA-like cavities @ 42 MV/mHigher Eacc by reducing Bpeak/Eacc
But TESLA who needs Eacc > 42 MV/m?
Carlo Pagani 21CSTS du SACM
CEA/Saclay, June 3, 2003
A few Comments on Priorities
BCP or EP?
BCP should be limited to applications asking for Bpeak < 80 mT (Eacc < 20 MV/m in TESLA-like cavities). Above 60 mT the expensive heat treatment @ 1400 °C has to be considered.
Because of the proven reduction of the field enhancement at the grain boundaries, EP should be preferred for applications asking for a very high peak magnetic field: Bpeak > 80 mT. But remember that complex geometries are still limited by cleaning (Epeak) and welding (Bpeak).
About Priorities
Most of the R&D effort should be concentrated on the understanding of the existing procedures, to make them fully reproducible and reliable.
Long term fundamental R&D should be mainly done in the framework of a collaboration between SACM and Universities taking advantages of their complementarities in term of culture and mandate.
Carlo Pagani 22CSTS du SACM
CEA/Saclay, June 3, 2003
What we do for TESLA - 1
Planned cavity R&D for TESLA in 2003The R&D activity is going slower then conceived because of:
Limited resources at DESY, in term of money and personnelReduced support from some historical partners of TESLA
A number of promising long term R&D activities are paying a highprice in term of possible effort: seamless cavity technology, superstructures, niobium coating, new materials, etc.In 2003 we are concentrating the effort to perform the followinghigh priority task:
Operate AC73 and ... in CHECHIA continuously for a few weeks.Final commissioning of the DESY EP Infrastructure using some 9-cell cavities of the 3rd production series.Treatment and vertical test of the first 9-cell cavities of the 4th production series (30 cavities, delivery starts in fall 2003).Improve the actually used EP parameters using single cells.More statistics on 800 °C baked cavities vs. 1400 °C UHV treated ones.Prepare more cavities for an EP accelerator module.
Carlo Pagani 23CSTS du SACM
CEA/Saclay, June 3, 2003
What we do for TESLA - 2
Priority on Linac TechnologyIn view of the construction of a large scale facility based on TESLA SC Linac Technology, we need to:
Analyze and Improve Accelerator Reliability, that is:Review TTF Linac components for performances and reliability Review the module design to reduce the assembly criticalitiesFocalize effort on critical itemsGive precise specifications for all minor ancillariesComplete the development of the 2 K quadrupole
Reach routinely 35 MV/m on cavities. This is due to:Understand and handle all the fabrication process:
Make the X-Ray FEL reliable and more performingAllow for higher c.m. Energies of the TESLA Collider
Carlo Pagani 24CSTS du SACM
CEA/Saclay, June 3, 2003
Conclusions and Suggestions
Given the outstanding tradition of SACM the fundamental R&D on SRF must be pursued and the allocated resources look adequate.
A strong connection with Universities is important for basic research and understanding. PhD students are the natural link between the two communities that have similar interests but different mandates.
Before their application, all new techniques for cavity treatment and handling should be deeply analyzed, comparing carefully the possible advantages with all the prices to be eventually paid. Remember that a new technique takes years to be reliably implemented.
It is crucial to reconstruct a much stronger international collaboration, as has been in the past through TESLA, to compare results, have suggestions a share the work to be done.